1. Field of the Invention
The present invention generally relates to the non-destructive computed tomography (CT) inspection of plies in composite materials and, in particular, a method for constructing a three-dimensional visualization of individual ones of such a ply using CT data.
2. Discussion of the Background Art
Over the years, the term composite has had several meanings regarding the use of two or more materials having different properties. More recently, in the aerospace industry, the term composite has come to be defined as a material containing a reinforcement such as fibers or particles supported in a binder or matrix material. Many composites may be used with the present invention including both metallic and non-metallic composites, however, the invention has a particular use with composites constructed with a unidirectional tape material and an epoxy resin matrix. A discussion of this and other suitable materials may be found in the "Engineering Materials Handbook" by ASM INTERNATIONAL, 1987-1989 or later editions, which are incorporated herein by reference. The composite blades and airfoils of the present invention are preferably of the non-metallic type made of a material containing a fiber such as a carbonaceous, silica, metal, metal oxide, or ceramic fiber embedded in a resin material such as Epoxy, PMR15, BMI, PEEU, etc. Of particular use are fibers unidirectionally aligned into a tape that is impregnated with a resin, formed into a part shape, and cured via an autoclaving process or press molding to form a light-weight, stiff, relatively homogeneous article having laminates within.
Composite materials are typically made by laying up or winding plies of material, injecting a resin into a container having the layed up material within, and then curing the resin. The process may produce anomalies such as waves or creases in some or all of the plies. Other types of so called "indications" are also of interest to composite manufacturers. It is therefore highly desirable to have techniques for investigating composites and displaying such indications in a manner by which the indications can be easily visualized. Such a visualization could be used for part conformance and particularly for inspections tests such as quality control on the assembly line or in the manufacturing process. Inspection using a non-destructive examination (NDE) method is best so as to minimize cost and time.
Computed tomography (CT) has long been a method for NDE inspection of metallic parts and human tissue. The high degree of homogeneity of composite parts poses a problem for inspection using CT apparatus and techniques. This is particularly true for indications, which tend to lie on ply surfaces. The problem is further exasperated when trying to inspect highly complex shapes such as composite fan blades of large gas turbine aircraft engines which have quite complex airfoil shapes. It is very difficult to determine the morphology or the extent of the indications.
CT systems, methods, and apparatus are well known in the art for inspecting large objects such as a gas turbine engine component, rocket engine component, or the like. They typically include a source of radiation and an associated detector both of which can be moved, relative to an object under inspection for purposes of reconstructing a cross-sectional area or slice through the object at a selected location on the object by means of penetrating the object with radiation and detecting the attenuation of the radiation caused by the object on an opposite side of the object from the radiation source. One X-ray inspection method and apparatus using Computed Tomography (CT) for which this invention was designed to be used with is explained in more detail in U.S. Pat. No. 5,119,408 which is incorporated herein by reference.
The present invention addresses the problems of NDE inspection of plies of composite parts using CT methods and, in particular, as applied to fan blades.